Organophosphorus esters which include a large number of important insecticides as well as fungicides, defoliants and fire retardants are inherently reactive chemicals and can form various types of covalent bonds with vital macromolecules in vivo directly or via conversion to electrophilic metabolites. Such interactions occur with a multiplicity of targets in the animal and are by no means limited to the well-known phosphorylation of cholinesterases. Depending on the compound, secondary interactions may lead to overt toxicological consequences such as delayed neuropathy, teratogenesis, delayed non-cholinergic mortality and carcinogenesis, or may result in more subtle biochemical imbalances which may become hazardous only under specific conditions. The liver plays a pivotal modulator role for these effects because of the high bioreactivity of organophosphates. This project seeks to analyze various factors controlling generation, interaction and sequestration of electrophilic metabolites in the liver. The ready biodegradability of organophosphates coupled with the recently realized wide variation of transhepatic behavior among these chemicals accentuates the need to understand functional heterogeneity of hepatocytes within the hepatic lobule (acinus). Recirculating autologous blood perfusion as well as forward and retrograde perfusion of the rat liver in situ, use of intralobular subpopulations of isolated hepatocytes and their cell-free preparations will provide a fresh means of analyzing the translobular behavior and the heterogeneity. Intralobular variations to be examined include titers of biotransformation enzymes, binding affinity for organophosphates and sensitivity to phosphates and phosphorothioates which may cause Beta-glucuronidase release, inhibition of mixed-function oxidases or cell death. Radiolabeled chemicals will be extensively used in all aspects of research including chromatographic analyses and autoradiography. Various organophosphorus esters of a wide range of lipophilicity and toxic characteristics will be employed. The rat will be the major experimental animal.